I understand part of his rationale, but it's flawed.
Because I believe in divinity (specifically Jesus Christ), I as a Christian would dare to theorize that because God spoke order into existence as it is, speaking the opposite of that (by an infinitely less powerful, but still power-imbued being) would bring about effects on the world. These effects produce the power behind what we know as incantations.
Similarly, potions only work when carried out using magical beings, or using matter from the body of a magical organism (moly, dragons' tears, fairy breath, eye of newt, etc.)
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)